Processes for the metal plating of polymers are known. U.S. Pat. No. 3,556,955 describes a process in which a polymer is conditioned with a strong acid such as sulfuric acid, sensitized in a solution of a reducing agent such as stannous chloride, activated by immersion in a noble metal salt solution and then placed in an electroless plating bath. A metal plating process is described in U.S. Pat. No. 3,896,252 in which a rubber modified unsaturated carboxylic acid or anhydride is contacted with a solution of ethylenediamine or 1,3-diaminopropane in an inert organic solvent that optionally also includes water in order to aminate the surface. Subsequently, a noble metal salt is added, followed by a reducing agent resulting in a metallized surface that can be metal plated using conventional techniques. U.S. Pat. No. 5,500,315 describes an electroless metal plating process using chemical etching to roughen a surface in order to chemically bond chemical groups to the surface that are capable of ligating with a metallic catalyst such as palladium.
A method of surface treating a substrate with a metal catalyst prior to plating is described in commonly assigned U.S. Pat. No. 5,153,023. The catalyst is dissolved in a solvent that does not dissolve or tackify the substrate, and the solution is coated on the substrate and dried. The coated substrate is heated to anchor the catalyst to the substrate surface. Commonly assigned U.S. Pat. No. 5,462,773 describes a method of preparing a polymeric substrate for metal plating by depositing an atomized stream of a precursor of a catalyst on the surface of a softened thermoplastic substrate and heating the deposited precursor to a temperature sufficient to decompose the catalyst, enabling the catalyst to penetrate the surface of the thermoplastic and become anchored in the substrate. Each of these earlier techniques involves treating the surface of a substrate to facilitate the adhesion of a metal plate layer thereon.
Components are commercially available that have substrates made of unfilled or, in some cases, lightly filled polymers with some or all of their surfaces coated in metal by electroless plating or electrolytic plating processes. In general, it has been found that certain unfilled polymers, such as acrylonitrile/butadiene/styrene (ABS), polycarbonates, polyimides, polyethersulfones, and the like, can be surface treated or otherwise pre-processed to electroless metal plate quite effectively. However, if a polymer contains a high load of filler material, problems with adhesion of the metal to the composite result when efforts are made to metal plate the composite. At least in part this is due to the manner in which the various components in the composite respond to the various plating processes. In the cases where the filler or fillers tend to populate the surface and thereby represent a disproportionately larger portion of the surface's composition when compared to the bulk composition, effectiveness of metal plating process may be affected to the point where the process simply does not work or the adhesion of the metal to the composite is compromised to the point where serious degradation to the utility of the plated polymer results. It would be useful to develop metal plated filled polymers having good adhesion of the metal plate layer or layers, as well as effective methods for their production.